FIG. 1A shows a circuit diagram 10 of the L6390 high voltage half bridge driver integrated circuit manufactured by STMicroelectronics. As shown in FIG. 1A, the circuit 10 includes a built-in bootstrap diode 12 (labeled as “bootstrap driver”) arranged between the low side supply voltage node VCC and the bootstrap supply voltage node BOOT, for connection with a bootstrap capacitor (not shown). FIG. 1B illustrates circuit connection of part of the L6390 high voltage half bridge driver integrated circuit 10 with an external bootstrap diode DBOOT and other external electrical components for realizing a bootstrap driver.
In the circuit 20 of FIG. 1B, during normal operation, energy is transferred from the low side power supply with nodes VCC and GND to high side supply decoupling capacitor CBOOT 24 between nodes BOOT and OUT, via the bootstrap diode DBOOT 22. However, in some applications it is preferable to integrate the bootstrap diode in the half-bridge driver integrated circuit for simplifying the application circuit. Generally, such integration requires a diode with high reverse breakdown voltage that is normally not available in typical integrated circuit process technology platforms. Accordingly, one solution is to use a diode emulator circuit having a high voltage device such as high voltage LDMOS device to emulate the function of a diode.
FIG. 1C illustrates circuit connection of part of the L6390 high voltage half bridge driver integrated circuit 10 with a built-in emulated bootstrap diode 32 and other external electrical components for realizing a bootstrap driver. The emulated bootstrap diode 32 includes a high voltage DMOS device arranged to be driven synchronously with the low-side driver (LVG) and connected with a diode in series. In the circuit 30 of FIG. 1C, during normal operation, energy is transferred from the low side power supply with nodes VCC and GND to high side supply decoupling capacitor CBOOT 34 between nodes BOOT and OUT, via the emulated bootstrap diode 32.
FIG. 2 shows another exemplary diode emulator circuit 40. The circuit 40 includes a high voltage LDMOS device 42. A source terminal of the device 42 is connected to the low side supply voltage node VCC; a drain terminal of the device 42 is connected to the bootstrap supply voltage node BOOT; and a gate terminal of the device 42 is connected with a low-side driver. The diode emulator circuit 40, while operable as a bootstrap diode, suffers from the following problems:
(1) An internal bootstrap gate driver circuit is required to enable a full (maximum) VCC voltage to reach the bootstrap capacitor CBOOT.
(2) The emulated diode can conduct only when the low side circuit is turned on.
In particular, the second problem means that proper initialization will be required before the high voltage half bridge integrated circuit can enter into normal functional modes. This issue can be addressed if a high voltage LDMOS device with an isolated body is present such that the body is connected to the source terminal of the high voltage LDMOS device 42 instead of to COM. Problematically, however, such a device is not readily available in most high voltage integrated circuit process platforms.
U.S. Pat. No. 5,666,280 and U.S. Pat. No. 7,215,189 further disclose some existing bootstrap diode emulator circuits. These circuits are typically operable with half-bridge driver integrated circuits.
It is an object of the invention to address the above needs, to overcome or substantially ameliorate the above disadvantages or, more generally, to provide a new or otherwise improved bootstrap diode emulator circuit.